This Excel spreadsheet uses the Sobocinski-Cornelius method to calculate the water breakthrough time. This method was published in 1965, and was derivied from laboratory tests. It uses these equations.

where

- B
_{o}is the oil formation volume factor - μ
_{o}is the oil viscosity (cp) - μ
_{w}is the water viscosity (cp) - φ is the porosity
- h is the oil column thickness (ft)
- h
_{p}is the perforated interval (ft) - Q
_{o}is the oil production rate (STB day^{-1}) - α is 0.5 if M <=1, or 0.6 otherwise
- M is the water-oil mobility ratio
- t
_{BT}is the time to breakthrough - t
_{D}is the dimensionless time (Sobocinski-Cornelius method) - Z is the dimensionless cone height
- ρ
_{w}is the water viscosity (lb ft^{-3}) - ρ
_{o}is the oil density (lb ft^{-3})